The responses of Pa, SPI, and SPEI to dry climate in alpine meadows of eastern Qinghai-Tibet Plateau

Using precipitation and temperature data from 33 meteorological stations around Gannan in 1965-2013, the percentage of precipitation anomalies (Pa), standardized precipitation index (SPI), and standardized precipitation evapotranspiration index (SPEI) were calculated. To select a suitable index to describe dry climatic factors in alpine meadows, we analysed the response of these indexes to drought. In addition, verification was conducted by comparing historical disaster statistics with the drought indexes. The correlation analysis of SPI, SPEI, and Pa with grassland normalized difference vegetation index (NDVI) showed that the reaction of Pa, SPI1, SPEI1, SPI3, and SPEI3 to precipitation was too sensitive; however, SPI12 and SPEI12 were slightly hysteretic. SPI6 and SPEI6 were both well suited to quantitatively evaluating the dry climatic factors in this area. Based on historical statistics, two drought indexes were somewhat better. These results provide effective data in support of further research on drought risk analysis in alpine grasslands.